Peripheral and central conduction abnormalities in diabetes mellitus

OBJECTIVES

To investigate peripheral and central somatosensory conduction in patients with diabetes.

METHODS

The authors recorded sensory nerve action potentials and 5-channel somatosensory evoked potentials (SEPs) with noncephalic reference after median nerve stimulation in 55 patients with diabetes and 41 age- and height-matched normal subjects. The authors determined onset or peak latencies of the Erb's potential (N9) and the spinal N13-P13 and the cortical N20-P20 components, and obtained the central conduction time (CCT) by onset-to-onset and peak-to-peak measurements.

RESULTS

Both onset and peak latencies of all SEP components were prolonged in patients with diabetes. The mean onset CCT in the diabetic group was 6.3 +/- 0.5 msec (mean +/- SD)-significantly longer than that in the control group (6.1 +/- 0.2 msec)-whereas no significant difference was found in the peak CCT. The amplitudes of N9 and N13-P13 components (but not N20-P20) were significantly smaller in the diabetic group. The peripheral sensory conduction velocity was also decreased in the diabetic group, but there was no significant correlation between peripheral conduction slowing and the onset of CCT prolongation.

CONCLUSIONS

Diabetes affects conductive function in the central as well as peripheral somatosensory pathways. The CCT abnormality does not coincide with lowering of the peripheral sensory conduction. The current results do not favor a hypothesis that a central-peripheral distal axonopathy plays an important role in development of diabetic polyneuropathy.

Cellular distribution of mucosa-associated lymphoid tissue with otitis media in children

This study examined mucosa-associated lymphoid tissue (MALT) in the eustachian tube (ET), middle ear (ME), and mastoid antrum (MA) in 163 celloidin-embedded temporal bones from children with or without otitis media. Otitis media was defined by the presence of histopathologically identified inflammatory cell infiltration in the mucosa or cavity of the ME. We found MALT in the ET in 30 cases (46.2%), in the ME in 19 cases (29.2%), and in the MA in 4 cases (6.2%) out of 65 cases of otitis media, and in the ET in 7 (7.1%), in the ME in 0, and in the MA in 0 out of 98 specimens without otitis media. No MALT appeared in any children under the age of 1 month. Immunohistochemical methods were used to investigate MALT in 12 horizontally cut temporal bones with OM. The follicular area contained OPD4-positive (helper-inducer T) cells and a few CD8-positive (cytotoxic and suppressor T) cells, whereas the parafollicular area contained OPD4-positive and CD8-positive T cells. CD57-positive (natural killer) cells were confined to the germinal center. CD30-positive (activated T and B) cells were observed throughout the follicles. A few CD15-positive (granulocyte, monocyte) cells were found in the follicles. Histopathologic and immunohistochemical findings were indistinguishable for MALT in the ET, ME, and MA. Our results suggest that MALT may be a mechanism for producing a rapid and massive local immune reaction to repeated bacterial infections via the ET.

Variations in vitamin D-binding protein (group-specific component protein) are associated with fasting plasma insulin levels in Japanese with normal glucose tolerance

The locus of the vitamin D-binding protein (DBP; also known as group-specific component protein or Gc) gene, chromosome 4q12, has been reported to be associated with glucose metabolism in several ethnic groups, including Pima Indians. We have recently reported the association of the DBP genotype with type 2 diabetes mellitus in Japan. The aim of this study was to investigate whether genetic variations of DBP have any influence on glucose metabolism without secondary effects of hyperglycemia or diabetes mellitus using 82 Japanese with normal glucose tolerance. The variations of the DBP gene (Gc 1F, 1S, and 2) were determined by PCR-restriction fragment length polymorphism. Fasting plasma insulin concentration and homeostasis model assessment, an index of insulin resistance, were significantly different based on the DBP genotype (P < 0.01 and P < 0.05, respectively). The people with Gc 1S-2 (5.73 +/- 2.57 microU/mL) and 1S-1S (5.30 +/- 3.46 microU/mL) had significantly higher fasting plasma concentrations than those with 1F-1F (2.84 +/- 1.67 microU/mL) (P < 0.01 and P < 0.03, respectively). There was no significant difference in plasma glucose concentration, body mass index, total cholesterol, triglyceride, and blood pressure. In conclusion, genetic variations of DBP are associated with insulin resistance in Japanese with normal glucose tolerance, which might contribute to the development of type 2 diabetes.

Stability of N20 onset or peak latency in median somatosensory evoked potentials

We analyzed onset and peak latencies of the N20 response of median nerve somatosensory evoked potentials (SEPs) in 21 healthy subjects by simultaneous recordings with noncephalic or ear reference from multiple scalp sites. The cortical onset was defined as the fork at which the contralateral parietal and frontal or ipsilateral parietal waves diverged. We found the N20 onset unchanged between noncephalic and ear reference recordings, or among the recordings around the contralateral centroparietal scalp. The N20 peak was prolonged when the recording position moved posteriorly. We suggest that N20 onset latency is more stable than N20 peak.

Lethal effect of the expression of a killer gene SMK1 in Saccharomyces cerevisiae

Expression of the SMK1 gene which encodes the yeast killer toxin SMKT is lethal in Saccharomyces cerevisiae. Effects of deletion and site-directed mutagenesis of SMK1 on the lethality and the secretion of the gene products were examined. Deletion of the interstitial gamma peptide or the C-terminal loop from Ala208 to the C-terminal Asp222 had no effect on the lethality. Those SMK1 products that lacked either the gamma peptide or the C-terminal loop were expressed in the cells but were not secreted into the culture medium, suggesting that these peptides may have a role in secretion or in protein stability. On the other hand, deletion of the signal sequence resulted in complete loss of the lethal activity. Entering the secretory pathway may be critical for the lethality. Further, deletion of the region from the C-terminus to Leu207 resulted in loss of the lethal activity. Leu207 is located at the C-terminus of the central strand of the beta-sheet structure of SMKT and its side chain is thrust into a hydrophobic environment between the beta-sheet and the alpha-helices. The result obtained upon substitutions of Ala, Ser or Glu for Leu207 suggested that the side chain of Leu207 stabilizes the hydrophobic environment that contributes to the overall structure of the SMK1 product.

Effects of activin A and follistatin on developmental kinetics of bovine embryos: cinematographic analysis in a chemically defined medium

The effects of recombinant human activin A and follistatin on the developmental kinetics of bovine presumptive zygotes matured and fertilized in vitro using time-lapse cinematography were investigated. The presumptive zygotes were cultured for 9 days in a chemically defined medium (modified synthetic oviduct fluid, control) and modified synthetic oviduct fluid supplemented with activin A or follistatin. Development under cine-recording conditions was similar to that in an incubator. Addition of activin A to modified synthetic oviduct fluid increased, while addition of follistatin decreased, the percentage of zygotes that developed to morulae and blastocysts. Follistatin significantly prolonged the timing of development to the 9-16-cell stage compared with the control and activin A media. Activin A significantly shortened the duration of the third cell cycle compared with the control, but follistatin significantly prolonged the fourth cell cycle compared with the control and activin A. Developmental arrest ('lag-phase') during the 4-8-cell stage was observed in 95% of embryos developed to more than the 9-16-cell stage in all treatments. The greater the number of cells at the onset of the lag-phase, the earlier the onset of the phase and the shorter the duration of the phase, the further embryos were able to develop by day 9 in all treatments. The number of cells at the onset of the lag-phase in the medium containing activin A was significantly higher than it was in control or follistatin-containing media. Moreover, activin A significantly shortened the duration of the lag-phase compared with follistatin. The present results indicate that activin A may enhance in vitro development of bovine embryos by improving developmental kinetics, especially by increasing the number of cells at the onset of the lag-phase and shortening the duration of this phase.

Effects of activin A and follistatin on developmental kinetics of bovine embryos: cinematographic analysis in a chemically defined medium

The effects of recombinant human activin A and follistatin on the developmental kinetics of bovine presumptive zygotes matured and fertilized in vitro using time-lapse cinematography were investigated. The presumptive zygotes were cultured for 9 days in a chemically defined medium (modified synthetic oviduct fluid, control) and modified synthetic oviduct fluid supplemented with activin A or follistatin. Development under cine-recording conditions was similar to that in an incubator. Addition of activin A to modified synthetic oviduct fluid increased, while addition of follistatin decreased, the percentage of zygotes that developed to morulae and blastocysts. Follistatin significantly prolonged the timing of development to the 9-16-cell stage compared with the control and activin A media. Activin A significantly shortened the duration of the third cell cycle compared with the control, but follistatin significantly prolonged the fourth cell cycle compared with the control and activin A. Developmental arrest ('lag-phase') during the 4-8-cell stage was observed in 95% of embryos developed to more than the 9-16-cell stage in all treatments. The greater the number of cells at the onset of the lag-phase, the earlier the onset of the phase and the shorter the duration of the phase, the further embryos were able to develop by day 9 in all treatments. The number of cells at the onset of the lag-phase in the medium containing activin A was significantly higher than it was in control or follistatin-containing media. Moreover, activin A significantly shortened the duration of the lag-phase compared with follistatin. The present results indicate that activin A may enhance in vitro development of bovine embryos by improving developmental kinetics, especially by increasing the number of cells at the onset of the lag-phase and shortening the duration of this phase.

An electrospray-ionization mass spectrometry analysis of the pH-dependent dissociation and denaturation processes of a heterodimeric protein

Electrospray ionization mass spectrometry (ESI-MS) was applied to the analysis of the dissociation and denaturation processes of a heterodimeric yeast killer toxin SMKT. The two distinct subunits of SMKT noncovalently associate under acidic conditions, but become dissociated and denatured under neutral and basic conditions. In order to understand the unique pH-dependent denaturation mechanism of this protein, a pH titration was performed by utilizing ESI-MS. The molecular ions of the heterodimer which possesses the highly ordered structure, were mainly observed below pH 4.6. However, the two subunits immediately dissociated at this pH. The spectra measured with various settings of the mass spectrometer indirectly demonstrated that the pH-dependent dissociation occurs in the liquid phase. The current result as well as the three-dimensional structure of SMKT suggest that the deprotonation of a specific carboxyl group triggers a cooperative dissociation process of this protein. In conclusion, the pH titration of a protein by ESI-MS is particularly effective, when the unfolding process or the biological function of the protein is related to the interaction with other molecules.

Direct detection of endogenous histamine in rat peritoneal mast cells by in-capillary derivatization high-performance capillary electrophoresis

A simple method for the detection of endogenous histamine in rat peritoneal mast cells was evaluated using on-line mode in-capillary derivatization high-performance capillary electrophoretic (ICD-HPCE) techniques, which were previously developed by our group [S. Oguri et al., J. Chromatogr. A, 787 (1997) 253-260]. The method involves a suspension of peritoneal mast cells (1 x 10(6) cells/ml of saline) collected from a male Wistar rat (eight weeks of age), which are directly introduced into the capillary tube from the anodic end by hydrostatic injection (at 25 cm height, for 2-20 s). When a high-voltage potential (25 kV) is applied to the capillary, which is already filled with the run buffer containing both a lysing reagent (SDS, sodium dodecyl sulfate,) and a derivatizing reagent (OPA, o-phthalaldehyde; NAC, N-acetylcysteine), histamine in the mast cells was detected at high-sensitivity level without further procedures. During ICD-HPCE, the mast cells injected in the capillary were lysed with the lysing reagent, free histamine released from the cell was labeled with the derivatizing reagent, and its derivative was electromigrated, separated and detected with a fluorescence detector (excitation wavelength at 340 nm, emission wavelength at 450 nm) in a fused-silica capillary (75 cm x effective length x 50 microm I.D.). The run buffer used was a 20 mM phosphate-borate buffer (pH 10) containing 20 mM SDS, 2 mM OPA and 2 mM NAC. This method was also examined with regard to the possibility of its use for determination of histamine at the single mast cell level.

Twin-to-twin transfusion syndrome with hydrops: a retrospective analysis of ten cases

We retrospectively studied 10 cases of twin-to-twin transfusion syndrome (TTTS) with fetal hydrops. TTTS was diagnosed sonographically between the 17-31 weeks of gestation. All twins were delivered by emergency cesarean section because of cardiac decompensation of one or both fetuses. The mean (+/-SD) age at diagnosis was 26.1 +/- 4.5 and the mean age at delivery was 28.8 +/- 2.0 weeks. Gestational age at birth was similar in survivors and nonsurvivors. However, surviving infants were diagnosed later in gestation (23.6 +/- 4.8 vs. 28.7 +/- 1.9 weeks; p < 0.01); and gestational age at appearance of hydrops were later in survivors (26.1 +/- 3.2 vs. 29.2 +/- 2.4 weeks; p < 0.05). Overall survival rate was 50% (10 of 20 infants). All survivors were delivered within 3 days after the appearance of fetal hydropic changes. Extrauterine treatment in earlier stages of TTTS might improve the outcome. Nevertheless, more aggressive intrauterine treatment should be considered in the most severe cases of TTTS developing before 24-25 weeks' gestation.

Characterization of the epitope on murine T-cell receptor (TCR) alpha proteins recognized by H28-710 monoclonal antibody

Antigen recognition by alphabeta T lymphocytes is mediated via the multisubunit T-cell receptor (TCR) complex consisting of invariant CD3-gamma,delta,epsilon, and zeta chains associated with clonotypic TCRalpha,beta molecules. In the current report, we evaluated the molecular basis for recognition of murine TCRalpha proteins by H28-710 monoclonal antibody (MAb), specific for the constant region of murine TCRalpha chains. H28-710 is widely used in the study of the TCR complex as it is the only reagent currently available that recognizes all murine TCRalpha proteins, regardless of their clonotype. These data show that H28-710 is useful for the immunoprecipitation of TCRalpha proteins not associated with CD3 subunits, and that H28-710 effectively recognizes denatured TCRalpha proteins synthesized in several different cell types. Most importantly, these results demonstrate that H28 binding involves a serine/threonine-rich region between amino acids 150-177 on murine TCRalpha polypeptides.

Esthetic replacement of a maxillary central incisor with an ITI 15-degree angled implant: a case report

Single-stage implants are frequently used, but their use in the anterior dentition has not been widely published. The purpose of this case report is to present the esthetic result of a single-stage implant to replace a maxillary central incisor, and to demonstrate the unconventional use of a 15-degree angled ITI implant. A 15-degree 12-mm hollow cylinder was placed with the angle reversed facially. The emergence profile of the adjacent roots was matched with the transmucosal portion, turning at the osseous crest. The implant was restored after 6 months with an ITI gold coping and transverse screw-retained crown. The gingival margin and the papillae were shaped by the transmucosal portion and the restoration. To date, the implant has been loaded for 24 months with an ideal soft tissue esthetic and radiographic appearance.

Prevalence of maternal cytomegalovirus (CMV) antibody and detection of CMV DNA in amniotic fluid

The prevalence of cytomegalovirus (CMV) IgG antibody was determined in 573 pregnant women in the first trimester. The overall prevalence of CMV IgG antibody was 77.5%. The rate of seropositivity was 67.7% in women < 25 yr, and increased with age to 85.7% in women 40 yr. These results imply that young women in Japan are at increased risk for primary CMV infection during pregnancy and that congenital CMV infection rates might increase in the future. We conducted a prospective study of 75 pregnant women who underwent amniocentesis for various indications to determine if CMV DNA could be detected in the amniotic fluid. None had symptoms associated with CMV infection, CMV IgM antibody, or seroconversion to CMV IgG antibody during pregnancy. CMV DNA was not detected in the amniotic fluid using a polymerase chain reaction assay. The 65 fetuses, including 3 sets of twins, were followed through birth. CMV DNA was not detected in urine samples obtained within the first 2 weeks of life. In conclusion, CMV DNA was not detected in the amniotic fluid of women who did not have CMV infection. These results, however, suggest that the negative predictive value of prenatal amniotic fluid analysis is high and that the presence of CMV DNA in the amniotic fluid has clinical significance for the diagnosis of congenital CMV infection if detected in pregnant women.

Distribution of psammoma bodies in the internal auditory canal and its extended areas in the human temporal bone

The internal auditory canal (IAC) and its extended areas of 27 normal human temporal bone specimens were investigated histologically for the distribution of psammoma bodies. A total of 145 +/- 25 (mean +/- SE) psammoma bodies were counted in series of every tenth 30-microm-thick section. Psammoma bodies were observed in the IAC and around the labyrinthine portion of the facial nerve (FN), the geniculate ganglion of the FN, and the posterior ampullary nerve in the singular canal. The number of psammoma bodies increases with age. We believe that psammoma bodies are a normal finding of aging in the IAC. The compression of the FN by psammoma bodies in the labyrinthine portion of the facial canal and the distribution of numerous psammoma bodies surrounding the posterior ampullary nerve in the narrow singular canal raise the questions of the involvement of psammoma bodies in the FN and in vestibular dysfunction and the presence of psammoma bodies in the subarachnoid space.

Inflammatory response to chronic otitis media in DiGeorge syndrome: a case study using immunohistochemistry on archival temporal bone sections

Immunohistochemical analyses were conducted on archival celloidin-embedded human temporal bone sections from an 8-month-old boy with chronic otitis media and DiGeorge syndrome. We employed antigen retrieval methods with saturated sodium hydroxide-methanol solution, microwave incubation, and proteolytic treatment to demonstrate the distribution of T-lymphocytes, B-lymphocytes, macrophages, and intercellular adhesion molecule 1 (ICAM-1) expression in the middle ear. B-lymphocytes and macrophages were observed predominantly within the middle ear mucosa. T-lymphocytes were rare. Further, ICAM-1 was expressed in the vascular endothelium of the lamina propria, as well as infiltrating mononuclear cells. This suggests that the expression of ICAM-1 can be induced in the middle ear with otitis media, even if T-lymphocytes are depressed in a cell-mediated immunodeficiency disorder such as DiGeorge syndrome.

[Genoepidemiology and pathogenicity of TT virus in Japanese men with history of intravenous drug abuse and tattoo]

Blood contamination has been proposed as TTV transmission. We studied the genoprevalence of TTV in Japanese men with history of intravenous drug abuse and/or tattoo. TTV was identified in serum by a polymerase chain reaction. TTV was detected in 89.7 percent of the men with history of intravenous drug abuse and/or tattoo, 74.4 percent of chronic hepatitis C patients, 78.0 percent of the chronic hepatitis B, and 65.8 percent of chronic hepatitis nonB nonC patients. Serum ALT levels of those infected with TTV alone were 27.2 +/- 17.5 IU/L. In the patients with chronic hepatitis C, serum ALT levels of those coinfected with TTV were similar to serum ALT levels of those without TTV infection. These results suggest that TTV causes no or mild hepatitis.

P-type ATPase spf1 mutants show a novel resistance mechanism for the killer toxin SMKT

SMKT, a killer toxin produced by the halotolerant yeast Pichia farinosa KK1, consists of alpha and beta subunits with folding remarkably similar to that of the fungal killer toxin KP4, a Ca2+ channel inhibitor. The budding yeast Saccharomyces cerevisiae is sensitive to SMKT. To understand the killing mechanism of SMKT, we isolated SMKT-resistant mutants of S. cerevisiae and characterized them. Five spf mutants (sensitivity to the P. farinosa killer toxin) fell into a single genetic complementation group, designated spf1. The SPF1 gene was cloned by complementation of the mutant phenotype. The SPF1 gene encodes a putative P-type ATPase of 1215 amino acid residues that contains 12 membrane-spanning regions. Gene disruption revealed that the SPF1 gene is not essential for viability but is required for the sensitivity to SMKT. The spf1 disruptant showed some phenotypes characteristic of glycosylation-defective mutants and secreted underglycosylated invertase. Fluorescence-activated cell-sorting analysis and indirect immunofluorescence microscopy showed that SMKT interacts with the cell surface of the resistant cells but not with that of sensitive cells, suggesting a novel resistance mechanism for this toxin. The glycosylation-defective phenotype and possible killer-resistant mechanisms are discussed in comparison with the Golgi Ca2+ pump Pmr1p.

Open sandwich ELISA with V(H)-/V(L)-alkaline phosphatase fusion proteins

The Sandwich ELISA is a widely used technique to measure antigen concentration. Recently, a novel ELISA based on the interchain interaction of separated V(H) and V(L) chains from a single antibody variable region (Fv) was proposed (Open Sandwich ELISA). Since it employs a single antibody recognizing one epitope, the assay requires, in essence, only one cycle of incubation and washing steps. To demonstrate this directly, we have constructed a recombinant gene fusion encoding the V(H) chain of an anti-hen egg lysozyme (HEL) antibody HyHEL-10 and Escherichia coli alkaline phosphatase (V(H)-PhoA). The same type of gene fusion using V(L) chain instead of V(H) chain (V(L)-PhoA) was also constructed and the proteins were obtained with an E. coli expression/secretion system. Open Sandwich ELISAs were performed using microtiter plates with immobilized V(L) or V(H) fragment, and V(H)-PhoA or V(L)-PhoA, respectively, as the detection reagent which was simultaneously added to each well with samples. As a result, HEL concentrations in the samples were determined after one round of incubation and washing steps, with a signal generated in a direct relationship to the concentration of HEL added to the reaction mixture. The minimum detectable HEL concentration was approximately 10 ng/ml, which was almost equal to the value previously obtained with plate-immobilized V(L) and V(H) fragment displayed on M13 phage. When the active-site mutant V(H)-PhoA(D101S) was employed instead of V(H)-PhoA and reacted at an optimum pH of 10, a significant enhancement in signal was attained.

Characterization of the solution properties of Pichia farinosa killer toxin using PGSE NMR diffusion measurements

The solution behaviour with respect to pH and NaCl concentration of the tertiary structure and propensity for aggregation of salt- mediated killer toxin (SMKT) from Pichia farinosa was examined using pulsed-gradient spin-echo NMR diffusion measurements. It was found that in 0.15m NaCl the tertiary structure of SMKT was constant below pH 5.0, with the native SMKT existing as an unaggregated heterodimer containing the beta-subunit in a compactly folded form. However, above pH 5.0 the beta-subunit dissociated and lost its compact structure, becoming a random coil with an approximately 37% increase in effective hydrodynamic radius. To determine the effects of NaCl concentration on the tertiary structure of SMKT, diffusion measurements were performed at pH 3.5 and NaCl concentrations up to 2M. Both the tertiary structure and aggregation state of SMKT were found to be insensitive to the salt concentration which indicates that the activity of the toxin is not a direct result of salt-protein interactions.

Secretion of a protoxin post-translationally controlled by NaCl in a halotolerant yeast, Pichia farinosa

The halotolerant yeast, Pichia farinosa KK1 secretes a killer toxin consisting of alpha (6.3 kDa) and beta (7.8 kDa) subunits, produced from a chromosomally encoded preprotoxin. In the presence of a high concentration of NaCl, a 26-kDa glycoprotein (gp26) that reacted with anti-beta-subunit antiserum was found to be secreted into the medium. Amino acid sequence analysis confirmed that gp26 is a protoxin generated by removal of the signal peptide from the preprotoxin. The purified gp26 did not have killer activity, suggesting that further processing is necessary for acquisition of this activity. Secretion of gp26 increased with increasing concentrations of NaCl in the medium and maximum secretion was observed at 2 M NaCl. Western blot analysis and RT-PCR showed that the secretion of gp26 is post-translationally controlled by NaCl.

Activin A and follistatin regulate developmental competence of In vitro-produced bovine embryos

The effects of activin A and/or follistatin on the development of bovine embryos were investigated. Presumptive zygotes matured and fertilized in vitro were cultured in a chemically defined medium (modified synthetic oviduct fluid medium; mSOF). Addition of 1-100 ng/ml of activin A to mSOF significantly increased the percentage of zygotes that developed to morulae and blastocysts (48-54% and 31-41%, respectively) compared with no addition (41% and 25%, respectively). In contrast, addition of 1-100 ng/ml follistatin significantly reduced the percentage of zygotes developing to morulae and blastocysts (29-31% and 17-20%, respectively) compared with no addition (41% and 28%, respectively). In a culture with 10 ng/ml of activin A, supplementation with the same concentration of follistatin neutralized the positive effect of activin A, while supplementation with 100 ng/ml of follistatin reduced the percentage of zygotes that developed. The total cell numbers in morulae and blastocysts were not affected by the addition of activin A and/or follistatin. The development-enhancing effects of activin A and the development-impeding effects of follistatin were observed when embryos were exposed to activin A or follistatin at a concentration of 10 ng/ml prior to the 9- to 16-cell stage. These results suggest that activin A and follistatin may affect bovine embryos until the third cell cycle and may play important roles in regulation of the developmental competence of bovine embryos.

High frequency oscillations in early cortical somatosensory evoked potentials

OBJECTIVE

To evaluate the characteristics of high frequency (HF) components of the early cortical somatosensory evoked potentials (SEPs).

METHODS

We recorded 8-channel SEPs from the frontal and left centro-parietal scalp after right median nerve stimulation with a wide band-pass (0.5-2000 Hz) and digitized at 40 kHz sampling rate in 12 healthy subjects. HF components were analyzed after digital band-pass filtering (300-1000 Hz). The power spectrum was obtained by a maximum entropy method.

RESULTS

HF oscillations (maximum power at 600-800 Hz) consisting of 5 to 8 peaks were discriminated from the preceding P14 far-field in all cases and their phases were reversed between the frontal and contralateral parietal regions. In addition, in subjects with a high amplitude central P22 potential in original wide-band recordings, a single HF oscillation with a maximum at the central region was present. Furthermore, this component showed no phase reversal over the centro-parietal area.

CONCLUSION

We therefore conclude that HF oscillations are superimposed not only on the tangential N20-P20 but on the radial P22 potential, and are generated from both tangential (area 3b) and radial (area 1) current sources.